There has been a continuing interest in the conversion of coal to useful liquid fuels for a great many years. One of the earliest fuels, coal oil, was derived by heating of coal to distil volatile hydrocarbons therefrom. With the development of large scale petroleum resources, interest in coal as a source of liquid fuels diminished for many years. There was renewed interest in coal as the source of liquid fuels for motor vehicle and engine operation in Germany with the shortages in petroleum supplies during the years of World War II, and much of the present technology in this field has its roots in developments during this period in Germany. The last decade has brought a greatly increased interest in apparatus and methods for recovering fuel from coal. Richardson, OIL FROM COAL, Noyes Data Corporation, Park Ridge, N.J., 1975, Chemical Technology Review No. 53, described and summarized the patents and literature and this technology generally as it existed at that date. Perrini, OIL FROM SHALE AND TAR SANDS, Noyes Data Corporation, Park Ridge, N.J., Chemical Technology Review No. 51, provides a similar survey of the technology for recovering oil from the two other major solid carbonaceous fuel sources, shale and tar sands. Howard-Smith and Werner, COAL CONVERSION TECHNOLOGY, Noyes Data Corporation, Park Ridge, N.J., 1976, Chemical Technology Review No. 66, surveyed the major processes and apparatus available for converting coal into other forms of fuel.
The conversion of coal to synthetic oil is described in Kirk-Othmer, ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, Second Edition, Supplement Volume, Pages 178-198 and the technology of coal generally is described in Kirk-Othmer, ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, Second Edition, Volume 5.
Storrs, U.S. Pat. No. 2,809,154, Oct. 8, 1957, describes apparatus and methods for treating coal to recover composition products therefrom by heating the coal in a substantially oxygen free atmosphere to release liquid decomposition products from the coal, maintaining the temperature such as to retain the liquid products in their phase, and prevent them from congealing or vaporizing. The coal, in the Storrs process, is formed into a continuous stream, passed through an elongate heating zone and substantially uniform heating of the particles throughout the depth of the bed, the liquid being extracted by withdrawing it from the bottom, through foraminous support member.
Bowman U.S. Pat. No. 3,475,279, Oct. 28, 1969, discloses apparatus and the methods for removing constituents from coal by forming a long horizontal bed of the coal, maintaining a slightly lower pressure at the bottom of the bed, enclosing the bed in a substantially oxygen free atmosphere, radiantly heating the top of the bed while maintaining the bottom of the bed cool enough to condense volatile materials distilled from the top of the bed.
Berg, working with the aforementioned Bowman apparatus and process, devised a modification thereof in which a flow of relatively low temperature gas was caused to flow through the bed to augment radiant heat transfer through the bed, U.S. Pat. No. 3,432,397, Mar. 11, 1969.
Bann U.S. Pat. No. 3,325,395, June 13, 1967, discloses a traveling grate method for recovering oil from shale in which a hearth layer of catalytic material, which promotes cracking of the distillate, is first charged on a grate as a hearth layer, the crushed oil bearing shale is then layered on this hearth layer, the combined bed is heated, and then the bed is divided again into the oil bearing shale and the hearth layer.
There have been many, many other apparatus and processes developed for extracting liquid fuel constituents from solid carbonaceous fuel sources, most of them uniquely applicable to coal, and some having broader application encompassing all forms of solid carbonaceous fuel sources. Other patents in this area are listed in the reference list at the close of the specification.